L12-ordered γ′ precipitates embedded in a fcc γ matrix impart excellent mechanical properties to nickel-base superalloys. However, these enhanced mechanical properties are lost under irradiation, which causes the γ′ precipitates to disorder and dissolve. We conduct an atomic-level study of radiation-induced disordering and dissolution at a coherent (100) facet of an initially ordered γ′ Ni3Al precipitate neighboring a pure Ni γ matrix. Using molecular dynamics, we simulate collision-induced events by sequentially introducing 10 keV primary knock-on atoms with random positions and directions. In the absence of thermally assisted recovery processes, the ordered Ni3Al layer disorders rapidly within 0.1–0.2 dpa and then gradually dissolves into the adjacent Ni layer at higher doses. Both the disordering efficiency and mixing parameter calculated from the simulations lie within the range of values found by experiments carried out at room temperature, where thermally activated diffusion is insignificant.

We have clarified the performance of two tungsten–helium analytical interatomic potentials, one of which, developed by Li et al., is a bond-order potential, and another, developed by Juslin et al., is a combination of embedded atom method potential and pair potential. Using these two potentials, we have simulated and made a full comparison of formation energy and migration energy of different defects including helium and vacancy, binding energies of helium and vacancy with helium-vacancy cluster, surface energy, as well as melting point, with reference to the corresponding results from the first-principles and experiments.

Swift heavy ion induced radiation damage is investigated for ceria (CeO2), which serves as a UO2 fuel surrogate. Microstructural changes resulting from an irradiation with 940 MeV gold ions of 42 keV/nm electronic energy loss are investigated by means of electron microscopy accompanied by electron energy loss spectroscopy showing that there exists a small density reduction in the ion track core. While chemical changes in the ion track are not precluded, evidence of them was not observed. Classical molecular dynamics simulations of thermal spikes in CeO2 with an energy deposition of 12 and 36 keV/nm show damage consisting of isolated point defects at 12 keV/nm, and defect clusters at 36 keV/nm, with no amorphization at either energy. Inferences are drawn from modeling about density changes in the ion track and the formation of interstitial loops that shed light on features observed by electron microscopy of swift heavy ion irradiated ceria.

Fission energy deposition in nuclear fuel has been experimentally observed to influence diffusion in uranium dioxide (UO2). This deposition is initially dominated by inelastic interactions with the electronic structure. Subsequently, energy is transferred to the lattice through electron–phonon (e–p) coupling resulting in a thermal spike and an associated pressure spike, which are presumed to contribute to diffusion enhancement. Molecular dynamics (MD) simulations were performed to investigate uranium diffusion enhancement in UO2 while varying the e–p coupling. The model was composed of 10 × 60 × 60 unit cells and used a Buckingham potential. A two-temperature model captured energy deposition in the electronic subsystem and its transfer to the atomic lattice. Experimentally, the fission enhanced diffusion coefficient (D*) of uranium in UO2 is observed to be athermal and proportional to fission rate density. For fission rate densities that are reported in experiment, the MD predicted D* was found to be on the order of 10−18 cm2/s, in reasonable agreement with experimental trends, and to decrease as e–p coupling was weakened.

This work is an overview of the physical approaches required for characterizing and understanding the long-term evolution of ceramics under irradiation. Because this subject is complex and has many ramifications, we have chosen to address the problem by looking at the behavior of a number of key ceramics. In the first part of this work, we present the physical mechanisms responsible for the production of primary defects, pointing out the main differences between metals, semiconductors, and insulators. In part two, we attempt to show how devoted experimental techniques can combine with transmission electron microscopy and x-ray techniques to provide a clearer picture of the long-term evolution of the microstructure of ceramics under irradiation. The last part of this work is devoted to discussing different approaches to explain and describe the long-term behavior of irradiated ceramics.

Candidate materials for actinide immobilization are subject to alpha-decay event doses that accumulate to values of more than 1020 alpha-decays per gram (tens displacements per atom, dpa) over the extended periods of geologic disposal. To evaluate the radiation-response of actinide-bearing materials, two experimental techniques have been used to accelerate the damage accumulation process: ion-beam irradiations and 244Cm-doping experiments. Based on modern characterization techniques, such as high-resolution transmission electron microscopy, and experimental results that involve ion-beam irradiation and chemical doping with highly active actinides, crystalline ceramics for the immobilization of actinides can be divided into three groups on the basis of their critical doses, Dc, i.e., the dose required for amorphization at 300 K: (i) low resistance to radiation damage accumulation (Dc ∼ 0.2 dpa) – murataite, Ti-perovskite, Fe-garnet; (ii) resistant (0.4 < Dc < 0.6 dpa) – Al-garnet, Ti–Zr-pyrochlore, Al-perovskite; and (iii) highly resistant (Dc > 0.8 dpa) – Zr-, Zr–Ti-, and Sn-pyrochlores. Phases with low critical temperatures (Tc below 600 K) will not become amorphous in a deep geologic repository, as long as the temperature remains between 300 and 550 K, but rather, they will remain crystalline. Only Zr-rich pyrochlore is fully resistant to radiation damage and will remain crystalline over the entire period of its disposal.

Investigations of the structural modifications induced in amorphous silica by ion irradiations in a wide energy range from ∼1 MeV to ∼1 GeV are reviewed. Several characterization methods such as infrared spectroscopy, chemical etching, dimensional measurements, and small-angle x-ray scattering have been used to measure the damage induced by individual ions and to analyze its evolution as a function of the energy released by the irradiating species. The comparison of the obtained results shows that high-energy ions lead to the formation along the ion trajectories of damaged zones (called ion tracks) above an electronic energy loss threshold depending on the ion specific energy. This threshold can be as low as ∼1.4 keV/nm for ion beams of 0.2 MeV/u and increases to ∼2.4 keV/nm at ∼5 MeV/u, in agreement with the velocity effect which predicts a narrower radial distribution of the deposited electronic energy with low-velocity ions than with high-velocity ions. Above these threshold values, track radii increase approximately with the square root of the electronic energy loss. In addition, for Au beams between 0.3 and 27 MeV, the generated damage exhibits a U-shaped dependence on the incident ion energy, suggesting a combined effect of the nuclear and electronic energy loss in this energy range. A unified thermal spike model taking into account the contributions of both energy losses allows to reproduce the whole experimental data.

Actinide-based nuclear ceramics, oxides particularly, are not only used as fuel in nuclear power reactors (uranium and plutonium) but are also used/envisaged as materials for electrical power sources in space probes (plutonium or americium). These actinides are all alpha-emitters, some having rather short half-lives. As a result of their strong alpha-activity, the actinide-based materials cumulate radiation damage and radiogenic helium. The stability of such materials needs to be assessed and understood for predicting the long-term stability of not only spent fuel in storage/disposal conditions but also of electrical power sources to be used in space probes. This paper describes the specific transmission electron microscope microstructure analyses of aged 238PuO2, 238Pu-doped UO2 (to simulate aged spent nuclear fuel), and of 241AmO2 samples (candidate electrical power source) and makes the correlation of the observed defects with other properties like helium thermal desorption and lattice parameter. It is shown that these fluorite structured materials resist to high alpha-damage levels and can accommodate large quantities of helium.

A systematic x-ray diffraction (XRD) study was performed on room-temperature Xe-irradiated and postirradiation annealed CeO2. Large scale XRD did not show any additional irradiation-induced phases upon irradiation. Depth profiling the CeO2 (111) diffraction peak over the 150 nm deep Xe-irradiated layer (400 keV, 1 × 1020 Xe/m2) by grazing incidence XRD indicated a lattice expansion at the irradiated layer. Postirradiation annealing (1 h at 1000 °C) in an oxygen-containing environment removed the observed XRD features. Electron energy loss spectroscopy (EELS) was performed for cross-sectional samples before and after postirradiation annealing. EELS showed that the Ce charge state changed from +4 to +3 at the CeO2 surface indicating the presence of O vacancies in both as-irradiated and annealed samples. EELS also indicated that the amount of O vacancies was reduced at the irradiated region by annealing. The experimental results are discussed based on electronic properties of CeO2, annihilation of oxygen vacancies, and evolution of irradiation damage.

Irradiation is one of the characteristic conditions that nuclear wasteforms must withstand to assure integrity during their service life. This study investigates gamma irradiation resistance of an early age slag cement-based grout, which is of interest for the nuclear industry as it is internationally used for encapsulation of low and intermediate level radioactive wastes. The slag cement-based grout withstands a gamma irradiation dose of 4.77 MGy over 256 h without reduction in its compressive strength; however, some cracking of irradiated samples was identified. The high strength retention is associated with the fact that the main hydration product forming in this binder, a calcium aluminum silicate hydrate (C–A–S–H) type gel, remains unmodified upon irradiation. Comparison with a heat-treated sample was carried out to identify potential effects of the temperature rise during irradiation exposure. The results suggested that formation of cracks is a combined effect of radiolysis and heating upon irradiation exposure.

Subcritical crack growth in SiC based composites is controlled by fiber creep processes. This lifetime limiting mechanism is of special concern under irradiation as it can enhance creep related mechanisms. To evaluate the impact of irradiation on the mechanical behavior of Tyranno SA3 fibers, in situ tensile tests were conducted on single fibers. These tests were conducted under irradiation with 92 MeV Xe23+ ions at 1000 °C for different ion fluxes and stress loads using a dedicated experimental facility. It has been found that irradiation induces time-dependent deformation of the fibers under conditions where thermal creep is negligible, i.e., 300 MPa and 1000 °C. Irradiation strain rate shows linear dependence with the ion beam flux and square root dependence with the applied stress. Finally, the irradiation creep compliance is estimated to be 1.01 × 10−5 MPa−1 dpa−1.

Single-crystalline diamond plates were implanted by He+ ions with a set of energies and fluences that ensure uniform radiation damage (RD) in a 670-nm-thick layer. Implantation is carried out at a wide range of fluences, which allows one to cover the range of RD levels from very low to complete graphitization of diamond. Using the measurement data on the bending of diamond plates and the surface swelling of the ion-implanted material, we calculate the mechanical stress and the density of diamond for various levels of RD. Diamonds with various levels of RD are investigated by the Raman scattering and optical transmission methods. We establish that, above the graphitization threshold, the diamond phase almost completely disappears as the RD level increases, while the fraction of sp2 material sharply increases. Such a material is unexpectedly ductile. It cannot be restored to diamond even by annealing under a pressure corresponding to thermodynamic stability of diamond.